Limited play optical devices with interstitial reactive layer and methods of making same

ABSTRACT

Methods and apparatus are provided for making an optically readable storage media in which the reading beam passes through a bonding layer configured with a reactive material that transforms from an optically transparent state to an optically opaque state after exposure to a predefined stimulus, thereby inhibiting access to the data encoded on the optically readable storage media. The method includes steps of synthesizing a blocked dye combining the blocked dye with a carrier material curing the resultant combination deblocking the dye to produce a reduced dye in the resultant bonding layer exposing the optically readable storage media with the reactive material in its bonding layer to a predetermined stimulus. In a further aspect of the present invention methods and apparatus are provided for making an optically readable storage media wherein the reading light passes through the bonding layer and the data encoded information is encoded on the L 1  substrate. In yet another aspect of the present invention methods and apparatus are provided for making an optically readable storage media with at least two mechanisms for limiting access to the encoded data of the optically readable storage media.

Priority is herewith claimed under 35 U.S.C. § 120 from Non-Provisionalpatent application Ser. No. 09/507,224 filed Feb. 18, 2000, which claimspriority to Provisional Patent Application Nos. 60/125,927 filed Mar.23, 1999 and 60/128,197 filed Apr. 7, 1999; Non-Provisional patentapplication Ser. No. 09/507,490 filed Feb. 18, 2000, which claimspriority to Provisional Patent Application Nos. 60/125,927 filed Mar.23, 1999 and 60/128,197 filed Apr. 7, 1999; and Non-Provisional patentapplication Ser. No. 09/608,328 filed Jun. 29, 2000, which claimspriority to Provisional Patent Application No. 60/143,474 filed Jul. 12,1999; and under 35 U.S.C. § 119(e) from copending Provisional PatentApplication 60/295,903 filed Jun. 5, 2001. The disclosure of all priorPatent Applications is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

This invention relates to optically readable data storage media and,more particularly, to methods, compositions, and articles of manufactureof optically readable data storage media wherein the data is accessiblefor a finite period of time.

BACKGROUND OF THE INVENTION

Optical discs such as CDs and DVDs are sold and rented to consumers. Thecontent of the optical discs may be music, movies, video clips, softwareor data The purchase price of CDs and DVDs can be high; this reflectsthe value of the information encoded on the discs, such as movies orsoftware, rather than the manufacturing cost of these optical discs.Frequently, content providers, such as movie studios or softwarecompanies, do not want to sell at a low cost copies of their informationthat will have a long lifetime in the marketplace. Consumers frequentlywant to access content information only for a brief period and at a lowcost. Rentals of CDs and DVDs enable consumers to access contentinformation at a lower cost than if consumers had to purchase the media,but the need to return the physical media is inconvenient. It would bedesirable to have limited play/expiring optical media that the usercould purchase at a low cost, would address the concerns of the contentproviders about lifetime of their content in the marketplace, and whichwould not have the disadvantage of having to be returned, as is the casewith videotape movie rentals today. It would also be desirable tomanufacture such optical media at low cost and with minimum changes toexisting manufacturing processes for optical discs. Finally, in orderfor the content providers to be willing to provide their content throughlimited play/expiring optical media, the mechanism that limits playingof the media should not he easily defeatable, enabling access to thecontent beyond the intended period of use.

Heretofore, the requirements of low cost, limited content lifetime,avoidance of rental returns, resistance to attempts to defeat, andminimum changes to existing manufacturing processes referred to abovehave not been fully met. What is needed is a solution thatsimultaneously addresses all of these requirements. One embodiment ofthe present invention is directed to meeting these requirements, amongothers.

Several approaches have been proposed to make a limited play (expiring)optical disc based on a layer that changes from a non-interfering(“transparent”) state where it does not interfere with the reliablereading of the information on the optical disc to an interfering(“opaque”) state where the layer interferes with the reading of the dataon the optical disc (e.g., see U.S. Pat. No. 5,815,484 assigned to Smithet al. and U.S. Pat. No. 6,011,772 assigned to Rollhaus et al.). Theinterference may be due to the layer becoming dark, reflective, highlybirefringent, pitting, bubbling, shattering, corroding, bending,changing refractive properties or combinations of these, among otherpossibilities.

Optical discs with such a layer changing from a transparent to an opaquestate in response to a stimulus such as exposure to oxygen in theatmosphere, or the light of the reading laser, can be used tomanufacture limited-play optical discs (such as DVDs) that becomeunusable in a predetermined way (such as within a certain period ofexposure to environmental oxygen). Such discs can find a variety ofcommercial applications, such as the viewing of a video by consumers ata moment chosen by the consumer and without the need to return theexpired optical disc.

The interfering layer that renders the disc unplayable by inhibiting thereading of the data can be applied via a variety of techniques to thesurface of an optical disc. Such an approach, however, has a number ofdisadvantages. For example, it may be defeated by finding a way toreverse the transition of the layer to an opaque state, such as exposingthe disc to a reducing chemical substance that reverses an oxidationreaction, or by entirely removing the layer through chemical means (suchas solvents) or mechanical means (such as polishing or grinding). Also,adding an additional layer can complicate manufacturing of the opticaldiscs, for example by requiring additional capital equipment andadditional steps in the manufacturing process, and thus can increase thecosts and/or decrease the yields for the manufacturing of optical discs.

A protective layer engineered to resist attempts to defeat the disc canbe applied on top of the interfering layer, an approach that has beenused by at least some of the present inventors. However, this introducesstill another step in the manufacturing process, further adding to costsand possibly further reducing manufacturing yields. Furthermore, sincethe protective layer would still be at the surface of the disc, it couldstill be removed by chemical means (such as solvents) or mechanicalmeans (such as polishing or grinding), or could be defeated by chemicalsubstances that could diffuse through the protective layer and reach thereactive layer.

As explained above, when manufacturing expiring optical discs, it isdesirable to employ a cost effective manufacturing process and to makediscs that are not easily defeatable. In addition, it is desirable forthe disc to make a rapid transition from the playable to the expiredstate. Among other benefits, this would reduce the variation of theplaying period among optical media players and drives, despite the factthat there is substantial variability in the ability of the players anddrives in the market to play discs with a given deterioration in theirphysical playability characteristics (such as the reflectivity to thelight of the reading laser).

SUMMARY OF THE INVENTION

Under a first aspect of the present invention limited play opticaldevices are provided with an interstitial reactive layer and methods ofmaking same.

Under a second aspect of the present invention a method is provided forauthoring a master to produce a substrate of a multi-substrate,optically-readable storage medium wherein a topology having a pluralityof pits and lands is used to create an inverted version of the topologyin which said inverted version of the topology is used as the topologyof the master.

Under a third aspect of the present invention a method is provided forforming a multi-substrate, optically-readable storage medium, whereinthe medium has information defined as a plurality of pits and lands onan upper substrate and said information is to be read by light beingtransmitted through a lower substrate wherein an adhesive layer bondsthe upper substrate and lower substrate together.

Under a fourth aspect of the present invention a data storage device isprovided having a first substrate having defined thereon a plurality ofpits and lands covered by a reflective material and a second substratewherein a bonding layer containing a reactive agent, which inhibitstransmission of light in response to a predetermined stimulus, residesbetween the first substrate and the second substrate.

Under a fifth aspect of the present invention an adhesive is providedfor bonding a first substrate and a second substrate, wherein saidadhesive comprises a carrier material and a reactive material thatrenders the data encoded substrate unreadable.

Under a sixth aspect of the present invention a mechanism is providedthat causes the data stored on an optically-readable data storage mediumto first become unreadable and second destroyed.

Under a seventh aspect of the present invention an optically-readabledata storage medium is provided having a first substrate and a secondsubstrate, wherein at least one of said first substrate and said secondsubstrate has information encoding features, and a bonding layer betweenfirst substrate and second substrate in which said bonding layercomprises a carrier material and a reactive material where said reactivematerial changes from a transparent state to an optically opaque stateas a result of a predefined stimulus.

Under a eighth aspect of the present invention a method making anadhesive is provided for bonding a first substrate and a secondsubstrate wherein a blocked dye is combined with a carrier material inwhich said blocked dye is subsequently unblocked resulting in thereduced form of the unblocked dye.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional view of select stages in theprocess of creating a physical stamper used in replicating DVD-5substrates.

FIG. 2 is a schematic cross sectional view of a single layer DVD-5 disc.

FIG. 3 is a schematic cross sectional view illustrating themanufacturing and reading of a standard DVD-5.

FIG. 4 is a diagram representing single sided single layer, single sideddouble layer, double layer single sided, and double layer double sidedDVD constructs.

FIG. 5 is a graphic depicting the index of refraction as a function ofsubstrate thickness for single layer and double layer DVDs.

FIG. 6 is a schematic illustrating the read-out possibilities forsingle-layer and dual-layer DVDs.

FIG. 7 is a schematic cross sectional view illustrating a modified DVD-5construct with the bonding layer in the optical path of the readinglaser.

FIG. 8 is schematic cross sectional view illustrating the manufacturingand reading of an altered DVD-5 construct with the bonding layer in theoptical path of the reading laser in which the mother stamper was usedto mold the L1 substrate.

FIG. 9 is a schematic cross sectional view illustrating the stamperreference plane of a standard DVD-5 construct wherein the pits and landsare molded in the L0 substrate.

FIG. 10 is a schematic cross sectional view illustrating the stamperreference plane of a modified DVD-5 construct wherein the pits and landsare molded in the L1 substrate.

FIG. 11 is a graphic depicting an atomic force microscope image of aDVD-5 father stamper.

FIG. 12 is a graphic depicting an atomic force microscope image of aDVD-5 mother stamper.

FIG. 13 is a graphic depicting an atomic force microscope image of theL1 layer of a modified DVD-5 that was molded from a mother stamper.

FIG. 14 is a schematic cross sectional view illustrating themanufacturing and reading of a modified DVD-5 in which the L1 layer wasmolded from a father stamper wherein the direction of the spiral trackwas reversed during mastering.

FIG. 15 is a schematic cross sectional view illustrating the stamperreference plane of a modified DVD-5 construct wherein the pits are abovethe surfaces of the lands and the lands are at the reference plane ofthe L1 substrate.

FIG. 16 is a schematic cross sectional view illustrating the stamperreference plane of a modified DVD-5 construct wherein the pits are abovethe reference plane of the L1 substrate and the lands are at thereference plane of the L1 substrate.

FIG. 17 illustrates a potential synthetic pathway for the synthesis oftriisopropylsilyloxycarbonylleucomethylene blue.

FIG. 18 illustrates the cyan reflectance density of optically readablestorage media coated with triisopropylsilyloxycarbonylleucomethyleneblue as a function of time in the presence 1,4-diazabicyclo[2,2,2]octane.

FIG. 19 is a graphic depicting the spectral absorption of metheleneblue.

FIG. 20 is a schematic cross sectional view illustrating a modifiedDVD-9 construct, wherein the L0 layer is partially metallized.

FIGS. 21A and 21B are graphics depicting Koch test results for amodified DVD-5 construct wherein the pits are molded as depressions inthe L1 substrate using a father stamper in which the direction of thespiral track is reversed during mastering.

DETAILED DESCRIPTION

Certain optical discs, such as DVDs, consist of two plastic halves(“substrates”), which are metallized and bound together with aninterstitial bonding layer. It would be desirable to use an interstitiallayer between the two substrates to interfere with the reading laser inorder to inhibit reading of the disc. This would result in a disc thatis more difficult to defeat, as the two halves of the optical disc wouldprotect the interfering layer. Using an interstitial layer as theinterfering layer still allows triggering the process of discexpiration. For example, polycarbonate, which is typically used tomanufacture DVD substrates, allows the propagation of oxygen that couldreach the interstitial reactive layer and trigger a reaction that causesthe expiration of the disc.

Furthermore, it would be desirable to use the bonding layer itself asthe interfering layer, for example by changing the chemical compositionof the bonding layer through the incorporation of a reactive substance.This could simplify the manufacturing of limited-play optical discsbecause no additional layers would be introduced, and attempting todefeat the limited-play mechanism by removing this layer could destroythe optical disc itself, as the bonding layer is critical to theintegrity of the optical disc. However, in certain types of opticaldiscs, such as a DVD-5, the bonding layer is not in the optical path.FIG. 2 illustrates a cross sectional view of the layers typical of aDVD-5 construct. Thus while the bonding layer could play part in anexpiration process for a DVD-5 that does not rely on direct interferencewith the reading laser (e.g., by corroding the reflective metal layerthat is in contact with the bonding layer), it would not be possible tomake this type of disc expire by transitioning the bonding layer to astate that prevents the reading laser from reading the data on the disc.Since it is often desirable to make the disc unplayable by means of aprocess that interferes with the reading laser, it is desirable to havea disc similar to a DVD-5 where the interstitial bonding layer is in theoptical path.

In limited use optical discs where the expiration process relies oninterference with the reading laser, the data encoding structures (suchas metallized pits on a polycarbonate substrate) typically are preservedin an expired disc, although the reading laser is prevented from readingthe encoded information. As long as these data structures are present,there is always the possibility of the disc being defeated by enablingthe reading laser to access the information. It would thus be desirableto have additional mechanisms that prevent recovery of the data, such aspermanently erasing the data by compromising the integrity of the datastructures on the optical disc.

These, and other, goals and embodiments of the invention will be betterappreciated and understood when considered in conjunction with thefollowing description and the accompanying drawings. It should beunderstood, however, that the following description, while indicatingpreferred embodiments of the invention and numerous specific detailsthereof, is given by way of illustration and not of limitation. Manychanges and modifications may be made within the scope of the inventionwithout departing from the spirit thereof, and the invention includesall such modifications.

A clear conception of the advantages and features constituting thepresent invention, and of the components and operation of model systemsprovided with the invention, will become more readily apparent byreferring to the exemplary, and therefore non-limiting, embodimentsillustrated in the drawings accompanying and forming a part of thisspecification. It should be noted that the features illustrated in thedrawings are not necessarily drawn to scale.

We now describe the different aspects of the current invention, andseveral corresponding embodiments and examples.

DVDs are the most common optical discs used for distribution of movies.DVDs are made from two bonded plastic substrates, typically referred toas L0 for the bottom substrate and L1 for the top substrate, where “top”and “bottom” refer to a DVD in a playing position where it is read fromthe bottom, as is the common convention. These substrates are moldedfrom materials such as polycarbonate, acrylic, or polyolefine, which isinjected in a molten form to a mold and pressed against a stamper. Theprocess of creating the physical stampers used in replicating the DVDsubstrates is referred to as Mastering. The following procedure is used,which is illustrated in FIG. 1:

-   -   1. Float glass blank 5 is polished and coated with a primer 10        to enhance adhesion with the photo resist layer 15.    -   2. Photo resist coating 15 is applied, baked, and then exposed        to the laser for recording. The formatted data signal is used to        modulate the cutting laser of a laser beam recorder (LBR)        machine which creates pits 20 in the glass disc.    -   3. The exposed glass is then developed leaving pits 20 and lands        25 across the surface.    -   4. This “Glass Master” then has a thin (110 nm) metal layer        sputter-applied to make the surface conductive for        electroplating.    -   5. The glass master is then placed into an electroplating        solution where nickel is formed to the desired thickness.        (Typically 0.300 mm).    -   6. This “Metal Father” (or “father stamper 30”) is then        separated from the glass master 35 and cleaned. At this step,        the metal father 30 could be used for the molding process, but        if the part gets destroyed or damaged in replication, the entire        process must be repeated.    -   7. Therefore, most manufacturers will grow “Metal Mothers” (or        “mother stampers 40”), which are negatives of the father 30.        Typically, four mother stampers 40 can be grown from one father        30 without quality degradation, and from each mother 40, up to 8        stampers (“sons 45”) can be grown.    -   8. Stampers get sent to replication facilities and mothers 40        are stored for reorders or replacement parts.

In the case of a DVD-5, which is a single layer disc illustrated in FIG.2, the L0 substrate 100 is covered with a thin reflective layer 105 ofaluminum by a sputtering process. This creates a metallic coatingbetween 60 and 100 angstroms thick (the L0 layer). The L0 substrate 100is then bonded 110 to a blank L1 substrate 110, as illustrated in FIG.3. For a DVD-9, which is a two-layer disc, the L0 layer is formed as avery thin, semi-reflective metal layer, and is typically made of gold. Afully reflective aluminum layer is formed on the L1 substrate (the L1layer). The two substrates are subsequently bonded with appropriateadhesive material, which forms a transparent bonding layer, to form theDVD-9 disc.

As seen in the DVD family illustration in FIG. 4, a DVD disc may containeither one or two information layers for each substrate, resulting todifferent types of disc capacities, such as DVD-5 200 (single sided,single layer, 4.7 Gbyte capacity), DVD-9 205 (single sided, dual layer,8.5 Gbyte capacity), DVD-10 210 (double sided, single layer, 9.4 Gbytecapacity), DVD-14 (double sided, one side single layer, one side duallayer, 13.2 Gbyte capacity), and DVD-18 215 (double sided, dual layer,17 Gbyte capacity).

A dual layer disc such as a DVD-9 205 must conform to the “DVDSpecifications for Read-Only Disc, Part 1 Physical SpecificationsVersion 1.0”, which require the following:

-   -   1. Total Disc thickness, including bonding layer 110, spacer(s)        and label(s), shall be 1.20 mm+0.30 mm/−0.06 mm    -   2. Index of refraction (RI) of the transparent substrate shall        be 1.55+/−0.10 The index of refraction of the spacer shall be        (RI of the substrate+/−0.10)    -   3. Thickness of the transparent substrate is specified as a        function of its index of refraction. Typically with        polycarbonate at RI=1.56, the thickness values for the disc        substrate would be 0.57 mm˜0.63 mm (see FIGS. 5A and 5B)        There is no specification for the DVD-5 200 and DVD-10 210        spacer layer (bonding layer 110), as long as the total disc        thickness conforms to the DVD specification and the half discs        (molded substrates) conform to RI related specifications as        above.

The information in DVDs is encoded in the pits 20 and lands 25 (dataareas that are not pits) that are molded into the substrates andsubsequently are metallized to form the corresponding data layer. Thepits and the lands are organized in a spiral track, which, in the caseof a DVD-5 200, is read in a clockwise direction beginning at the insideof the disc and proceeding towards the outside of the disc. Thereference area of the disc that is not occupied by data is used fortracking of the reading laser. The reading laser, which has a wavelengthof 630–650 nanometers in vacuum, is focused on the L0 layer 100 of aDVD-5 200 or DVD-9 205, or on the L1 layer 115 of a DVD-9 by penetratingthrough the semi-reflective L0 layer 100, and it is reflected back to aphoto detector. During transitions from a pit 20 to a land 25 or viceversa, interference patterns develop, which are detected by the photodetector and result in changes in its electrical output. These changesin the electrical output of the photo detector allow the player to readthe information recorded on the DVD.

Dual-layer discs, such as DVD-9s 205, typically utilize one of twomethods for read-out of the disc information:

A dual-layer Parallel Track Path (PTP) disc 299 will have a Lead-in 300and a Lead-out 305 area on both layers, as illustrated in FIG. 6. Foreach layer, the lead-in 300 area is located at the inner radius of thedisc, and lead-out 305 area is located at the outer radius of the disc.This layout structure is comparable with the layout of the single layer320 disc. Reading of the data is done, as in a DVD-5, 200 from the innerradius of the disc to the outer radius, for both layers. With properauthoring of the content on the disc, the PTP method can allow quickaccess from layer to layer, for example in order to provide backgroundinformation and commentary in one track along with the movie in theother track.

A dual-layer Opposite Track Path (OTP) 325 disc, also illustrated inFIG. 6, offers the possibility of seamless continuation of the playbackfrom the L0 100 to the L1 115 layer. The first information layer (L0)100 starts with a lead-in area at the inner radius of the disc and endswith a so-called middle area 330 at the outer radius. The secondinformation layer starts with a Middle Area 330 at the outer radius andends with a lead-out 300 area at the inner radius of the disc. Readingthe data 335 stored on the disc will start at the inner radius of thefirst information layer and proceed until the Middle Area 330 of thislayer is reached. Then a switch over to the Middle Area in the secondinformation layer is made, in order to continue reading of the data fromthe outer radius up to the lead-out 305 Area in the inner radius of thesecond layer (L1) 115.

Single Layer Optical Discs

One embodiment of the present invention is an optical disc similar to aDVD-5 where, unlike a standard DVD-5, the interstitial layer 400typically used as the bonding layer 401 is in the optical path 405 ofthe reading laser (e.g., see FIG. 7). In one embodiment of the presentinvention (labeled below as “Special DVD-5 design #1”), this disc ismanufactured by inverting the reflective layer 410 of a standard DVD-5,and reading the information through the non-information-bearingsubstrate 415 and the bonding layer 401. In another embodiment of thepresent invention (labeled below as “Special DVD-5 design #2”), thedirection of the spiral track is inverted during mastering, theinformation bearing substrate is flipped “upside down”, and theinformation is read through the non-information bearing substrate 415and the bonding layer 401. In this type of optical disc, the bondinglayer 401 is an integral part of the optical path 405 of the readinglaser. Even though the structure of the “Special DVD-5” disc describedherein differs from a standard DVD-5, a player would play this disc asif it were a standard DVD-5.

This embodiment of the present invention has significant advantages interms of allowing the manufacturing of a low-cost “limited-play” opticaldisc that is resistant to attempts to defeat it. In particular, becauseit does not incorporate any additional layers compared to a standardDVD-5, it can be manufactured on equipment designed to manufacture DVD-5discs with minimal changes to that equipment. Furthermore, because thebonding layer 401 is in the optical path, 405 modifying that layer tointerfere with the reading of data in response to a predeterminedstimulus results in a disc that is very difficult to defeat, as theinterfering layer 400 is protected by the two substrates 415 and 420,respectively of the optical disc. For example, grinding the interferinglayer 400 off the disc is impractical, as it would most likely destroythe disc. Similarly, attempting to compromise the bonding/interferinglayer in other ways is likely to destroy the structural integrity of theoptical disc.

We now describe in detail the manufacturing of three embodiments of thecurrent invention, which we label as “Special DVD-5” designs 1, 2 and 3.

Special DVD-5 Design #1

In one embodiment of the invention, the above process is modified byusing the mother stamper to replicate the L1 disc substrate 420. FIG. 3shows how the stamper or father is used to mold a normal single layerDVD-5 substrate. FIG. 8 illustrates manufacturing this embodiment of thecurrent invention by using the mother stamper 40 and creating a discwith the bonding layer 401 in the optical path 405.

In a normally molded standard DVD-5 information is encoded on the L0 100side with “pits” 20 and “lands” 25 molded on the L0 substrate 100 andmetallized with a reflective metal coating, 105 as illustrated in FIG.2, FIG. 3 and FIG. 9. In one embodiment of the current invention, themother stamper 40 is used to mold the L1 side 420 as shown in FIG. 8.This side is subsequently metallized and bonded with a blank L0substrate, 415 leaving the bonding layer 401 in the optical path, 405 asshown in FIG. 10. Using the specified layer thickness of 0.055mm+/−0.015, the thickness of the L0 substrate 100 is targeted at 0.55 mm0.57 during molding, to yield a focal length of the disc thickness(including the bonding layer) consistent with standard DVDspecifications, allowing the player to be in the normal focusing rangefor reading a L0 layer 100. Thus the player interprets the disc as astandard single layer DVD-5. Field experience has shown that spacerlayer thickness can be maintained at 0.045˜0.065 mm consistently inproduction. This controlled variation in production along with thereduced thickness of the molded disc keeps the focus and optics withinthe specifications set by the DVD licensing authority and the hardwaremanufacturers.

For the replication facility, most applications would remain unchangedin the actual pressing and bonding portions of production. The mainareas of change would be in the LBR (laser beam recording) anddeveloping areas of mastering. Typically, masters are cut with largerpit volumes to compensate for plastic shrinkage and replicationinefficiencies. The ratio of pit to land areas on a disc is measured bya term called asymmetry. Because asymmetry is a ratio of pit to landarea, and because for each pit area, typically defined by I3 to I14 pit,there is an equal and opposite land area I3 to I14 land, typically it iseasier for manufacturers to target a positive asymmetry (larger pitarea) to account for loses in replication to the plastic substrate. Forexample, the master may be cut with a positive 10˜12% for asymmetry,while the end result from molding may be 5˜7%. The specification for thedisc substrate is: −0.05≦asymmetry≦+0.15. In the case of DVD discs, apositive asymmetry represents a larger pit volume compared with the landarea.

For this embodiment of the invention, it may be desirable to change theasymmetry set point on the LBR to produce a higher asymmetry value onthe father stamper while subsequently increasing the asymmetry on themother stamper used for molding. Asymmetry can be changed on the masterby modifying the power of exposure, focusing intensity and offset,developing time/endpoint detection, or baseline (control of how fast thelaser diode cuts the laser exposure beam off between exposure). Thereare many other possible ways to control asymmetry, but the basic processor set point control would be the easiest to implement. This process ofmolding from the mother stamper would also eliminate the need to growadditional stampers and the subsequent yield loses attributed to thefamily process.

In this embodiment of the invention, the pits 20 are molded in the L1layer 420 using a mother stamper, 40 and as a result the surface of thepits 20 is elevated relative to the reference plane 450 of the L1 layer420 as illustrated in FIG. 10. This reference plane 450 is typicallyused for tracking by the disc player (tracking area). By contrast, in anormal DVD-5 the pits 20 are molded as cavities in the L0 substrate 100as illustrated in FIG. 9. Using the common convention of describing adisc as if it is in a play position where it is read from the bottom,and a convention that we will follow hereinafter unless otherwisespecified, in a normal DVD-5 the pits 20 are lower than the referenceplane 450, while the lands 25 are at the reference plane 450 (see FIG.9). In the embodiment of the invention described above the blank L0substrate 415 and the bonding layer 401 are below the L1 substrate 420in the optical path 405 of the reading laser, and the surface of thepits 20 in the L1 substrate 420 is below the reference plane 450 whilethe lands 25 are at the reference plane 450 (see FIG. 10). Note thatthis construction requires the pits 25 to be molded in an unconventionalway (they protrude from the reference plane 450 of the disc), which isachieved by molding the L1 substrate 420 from a mother stamper 40. FIG.11 shows an Atomic Force Microscope (AFM) image of a Father stamper 30for a DVD-5, FIG. 12 shows an AFM image of the corresponding Motherstamper 40, and FIG. 13 shows an AFM image of the L1 layer of a SpecialDVD-5 Design #1, molded from the Mother stamper 40.

This molding required for this embodiment of the invention can presentcertain challenges. In a typical injection molding process, the polymermaterial flows around the pits 20 on the stamper, which are raised fromthe reference plane 450. This is easier than to mold from the mother,where the polymer material must flow into cavities that will form thepits 20 on the separated part. As the material flows over the surface ofthe mother stamper 40, the molecular chains cool off through contactwith the relatively colder reference surface of the stamper. After themold is completely filled, then pressure must be applied to bend andforce the cooler polymer material into the pit 20 cavities. Althoughthis method is capable to reproduce discs within the specifications of astandard DVD-5 configuration, the molding process is more difficult.However, one skilled in the art can address such challenges by adjustingthe process characteristics of the molding machine, e.g., by increasingmold surface temperature and cycle time. Alternatively appropriatematerials with higher melt flow rate could be used, such as PMMA or highmelt flow rate polycarbonate. For example, General Electric's SPOQresearch grade polycarbonate has twice the melt flow rate of standardgrade polycarbonate.

As long as the index of refraction (RI) of the bonding adhesive used isapproximately equal to the RI of the L0 substrate 415, the thickness ofthe bonding layer 401 is uniform, and the thickness of the L0 substrate415 has been adjusted to compensate for the presence of the bondinglayer 401 in the optical path 405 of the reading layer, the player willnot be able to distinguish Special DVD-5 Design #1 from a standardDVD-5. Experience has shown that playable discs can be manufactured evenwithout these adjustments, because most players will play discs that donot fully conform to the DVD specification, as long as the departurefrom the specification is not excessive.

EXAMPLE 1 Special DVD-5 Design #1

A father stamper 30 was mastered with slightly increased symmetry(positive asymmetry=larger pits 20 compared to lands 25). The asymmetrycan be increased or decreased many ways. The simplest method and the oneused for this design, was to increase the development time (endpointdetection set point) to overdevelop the pits 20. By lengthening thedevelopment process, the pit volume surrounding, that which was exposed,will increase in volume causing a shift to positive asymmetry.

A mother stamper 40 was grown from the father stamper 30 as with anormal family process. Disc substrates were molded from the motherstamper 40, taking advantage of the larger indentation caused by thepositive asymmetry. The larger pits 20 that resulted from molding withthe mother 40 helped to compensate for the additional shrinkage of thepit 20, which is now an extremity to the body of the substrate, ratherthan a cavity as in the standard molding process. Typically, the moltenplastic flows around the pits 20 in a normal (father 30 or son 45)stamper like a river flows around a hill. As the level rises, the hillor the pit 20 will be covered. As the molten plastic flows across thecooler stamper surface, a skin layer forms right on the surface thatacts as a heat insulator. This allows for the plastic to maintain itsflow rate necessary to form the pit volume without undue stress orcooling. In the case of Special DVD-5 design #1, the plastic has to flowinto the indentations of the mother stamper 40, rather than around thebumps of a father/son stamper 30 and 45 respectively. This is difficultbecause as the plastic flows across the surface of the mother stamper40, it again forms a skin layer on the surface. Then as the mold volumeincreases with continued injection and packing/holding time, the moltenplastic must be forced into the indentation. Because this skin layer issolidified typically below the glass transitional temperature of theplastic, the material does not free flow into the indentation. Becausethe pit-forming plastic in the L1 substrate 420 of Special DVD-5 design#1 is not in the optical path of the reading laser, the material can befilled with greater force without the concern for birefringence andresidual stress, although there is a limit to the pressure due towarping (tilt) caused by excessive packing pressure on the plastic. Inthis example, the combination of larger indentations in the motherstamper 40 as well as increased mold temperatures assisted inreplicating the desired pits 20. Typically, in direct water injectionsystems for the mold heating and cooling, safety interlocks of 120° C.max temperature limit the temperature of the water. By using a 50/50solution of glycol and water, the temperature can be effectively run ata max temperature of 130° C. This added temperature assists in keepingthe skin layer in the molten state, close to its glass transitiontemperature, which facilitates the replication of L1 substrates 420 forSpecial DVD-5 design #1. Also, the mother stamper 40 must be filledquickly with molten plastic in order to prevent skinning on the surface.

L1 substrates 420 were molded as above using a mother stamper 40. FIG.13 shows an Atomic Force Microscope (AFM) image of an L1 layer 420molded from a mother stamper 40. FIGS. 11 and 12 show AFM images of thefather 30 and mother 40 stampers used in the process. For these discs tobe formed, it was necessary to raise the melt temperature from 360° C.to 390° C. while maintaining a mold temperature of 121° C. compared tothe standard of around 100° C. The clamp force was set at maximum of 30tons and the filling time was decreased from 0.13 to 0.09 seconds. Theseparameters were adjusted until the proper pit 20 formations wereachieved.

The molded L1 substrates 420 were bonded using optical grade UV curableDVD adhesives, as used in DVD-9 production, to blank L0 substrates 415,to manufacture design #1 of the Special DVD-5. L0 substrates 415 weremolded at a thickness of 0.55˜0.57 mm (i.e., 30˜50 micron thinner thanstandard DVD halves) to compensate for the bonding layer in the opticalpath, thus preserving the same focal depth for the information-carryinglayer as in a standard DVD-5.

Special DVD-5 Design #2

The electronics of optical media drives, including DVD players, aretypically designed to read the information contained in a layer on thedisc by identifying the interference patterns caused by the transitionsfrom a “land” 25 to a “pit” 20 in that layer. The pits 20 are oftenmolded with a height approximately equal to, and typically somewhat lessthan, one quarter of the wavelength of the reading laser. For example,in DVDs the typical wavelength of the reading laser is 635–650nanometers (in vacuum), or 410–420 nm in a material with RI=1.55 (whichis typical of the materials used to manufacture the DVD substrates), andthus the height of the pits 20 in a standard DVD-5 should beapproximately 100–105 nanometers. Consequently, a transition from a land25 to a pit 20 or vice versa corresponds to a change to the path of thereading laser of approximately one half wavelength, or a phase change ofapproximately 180 degrees. Two identical waves with a phase differenceof 180 degrees will interfere with each other and cancel out, and theelectronics of the optical drive are designed to detect the resultinginterference patterns. Using the standard convention of the disc beingread from below, in a standard DVD-5 the surface of the pits 20 is belowthe surface of the land 25, and a transition from a land 25 to a pit 20is a “down” transition, while a transition from a pit 20 to a land 25 isan “up” transition. If the height of the pits 20 is one quarter of thewavelength of the reading laser then a transition from a land 25 to apit 20 in a standard DVD-5 is a “down” transition that corresponds to aphase change of +180 degrees, and a transition from a pit to a land 25is an “up” transition that corresponds to a phase change of −180degrees. If an “up” and a “down” transition differ by 360 degrees, as inthe case described above, their effects will be identical. Oneimplication of this is that the pits 20 of a DVD-5 could be molded inthe opposite direction, i.e., with the pit surface approximately onequarter wavelength above the land 25 surface, and the electronics of theoptical disc player are unlikely to be influenced by whether a detectedtransition is in the “up” or “down” direction, i.e. whether a pit 20area is higher or lower than the land 25 area.

In a standard DVD-5, the laser pick up will read through the L0substrate 100 focusing on the pits 20 aligned in a spiral track. Therotation of the disc would be in the counterclockwise direction (as seenfrom the side of the reading laser), and the spiral track would be inthe clockwise direction. Given that the pit 20 direction can be reversedwithout changing the electrical signal seen by the player, in anotherembodiment of the current invention the pits 20 are molded asdepressions 500 into the L1 substrate 420, by employing a normal(father/son) DVD-5 stamper 30/45, as illustrated in FIG. 14. Thedirection of the spiral track is reversed during mastering, as the discwill be read from the side of the bonding layer 401, rather than throughthe substrate as in a standard DVD-5. The resulting disc has informationencoded as a DVD-5, although the pits 20 are formed in the L1 layer 420:the surfaces of the pits 20 are above the surfaces of the lands 25, andthe lands 25 are at the reference plane of the L1 layer 420, asillustrated in FIG. 15. The pit 20 width, length, height, and shape givethe corresponding HF signals needed to decode the data on the DVD. Thesignals are encoded utilizing an eight-to-fourteen modulation (EFM)signal. The pit 20 edges and slopes of the sidewalls serve todistinguish the logical transition of 0's and 1's. This results in pit20 length units measured as 3 units long to 14 units long, which set thefrequency limits of the EFM signal, read from the disc. This measurementis commonly referred to as 3 T–14 T signal with T referring to a periodof time. As long as the pits 20 are replicated in standard fashion, theplayer will still be able to distinguish the pit 20 start and endposition, while reading from the reverse side, to correctly identify itsdata identity. In many circumstances this will be the preferredembodiment of the invention, as it does not require molding from themother stamper 40, as is the case with Special DVD-5 design #1 above.

The actual height of the pits 20 in a standard DVD-5 is typicallysomewhat less than one quarter wavelength of the reading laser. This isintended to avoid complete cancellation of the reflected laser during apit-to-land transition, which facilitates the functioning of playerelectronics. For example, a value of 0.88*(laser wavelength)/4 issometimes recommended, i.e. approximately 90 nanometers for a materialwith RI=1.55. Thus it may be desirable to mold the pit 20 surfaces inthis embodiment of the current invention somewhat higher than onequarter the wavelength of the reading laser, so that the change in thepath of the reading laser during a transition from a land 25 to a pit 20in the special DVD-5 design #2 will be exactly one wavelength longerthan the corresponding change in a standard DVD-5. For example, if thereading laser wavelength is 650 nanometers (i.e., 420 nm in apolycarbonate substrate of RI=1.55), and the pits in a standard DVD-5are 90 nanometers, the pits 20 in this embodiment (Special DVD-5 design#2) can be molded at 120 nanometers, i.e., one half wavelength (210 nm)from the position of the pit 20 surface in design #1.

EXAMPLE 2 Special DVD-5 Design #2

A special stamper for molding L1 substrates 420 for Special DVD-5 Design#2 was produced through a modified mastering process, where thedirection of rotation of the laser beam recorder turntable was reversedduring the cutting process, resulting in a spiral tracking path in theopposite direction from that in a normal DVD-5. This stamper wasproduced by forcing the turntable to rotate in the reverse directionfrom cutting a normal DVD-5, while the content information was fed tothe laser beam recorder as a DVD-5 image. The scanning velocity that isnormally preset for DVD formats was manually set to the velocity of 3.49m/s typical in DVD-5 mastering. L1 substrates 420 were then molded onstandard molding machines set up for DVD-5 fabrication.

Some of the molded L1 substrates 420 were bonded using optical grade UVcurable DVD adhesives to blank L0 substrates 415, to manufacture design#2 of the Special DVD-5. As in Example 1, the L0 substrates 415 weremolded at a thickness of 0.55˜0.57 mm (i.e., 30˜50 micron thinner thanstandard DVD halves) to compensate for the bonding layer 401 in theoptical path, thus preserving the same focal depth for theinformation-carrying layer as in a standard DVD-5. To bond the discs,the machines were placed into a DVD-9 production mode and thesemi-reflective metallizer for the L0 layer was taken offline. Then thecure time was adjusted to compensate for the decrease in cure exposureneeded due to the missing semi-reflective layer. Curing was basicallyset for a DVD-5 disc, and the disc was flipped to cure through the L0layer. This function is typically reserved for DVD-9 production.

The discs were then tested with a Koch DVD testing system and played infour different DVD players. They performed indistinguishably fromregular DVD-5 discs, as illustrated in FIGS. 21 and 22. Also, the discsplayed with no errors in an additional three DVD players and two DVD-ROMdrives.

Some of the molded substrates were used to manufacture discs with areactive bonding layer (see Example 9).

Special DVD-5 Design #3

The electronics of optical media drives, including DVD players, can bedesigned to read the information contained in a layer on the disc byidentifying pits 20 and lands 25 in that layer based on the absoluteand/or relative elevation of these pits 20 and lands 25, thusdistinguishing between an “up” and a “down” transition in theinformation encoding layer, but without being influenced by theelevation of the pits 20 and lands 25 relative to the reference plane450 of the layer. Thus in another embodiment of the current invention,during mastering the direction of the spiral track is reversed and alsothe pits 20 and lands 25 are reversed, so that the pits 20 become lands25 on the resulting stamper 30, and lands 25 become pits 555. The L1substrate 420 is then molded by employing 550 a normal (father) stamper30 and is bonded to a blank L0 substrate 415. The resulting disc hasinformation encoded as a DVD-5, the relative elevation of pits andlands, and the “up” and “down” transitions in the information encodinglayer, are identical to a DVD-5. Specifically, the surface of the pitsis below the surface of the lands. However, while in a standard DVD-5the surface of the lands is at the reference plane of the L0 layer, inthis embodiment it is the surface of the lands 560 (corresponding topits on a standard DVD-5) that is at the reference plane of the L1layer, with the pits 565 (corresponding to lands on a regular DVD-5)being above this reference plane, as illustrated in FIG. 16.

The Reactive Bonding Layer

Another embodiment of the present invention is having a reactivematerial incorporated in an interstitial layer. In one embodiment, theinterstitial layer is the bonding layer of the disc.

In one embodiment of the invention, the stimulus triggering the reactionis exposure to atmospheric oxygen. Upon exposure to oxygen, a reactivematerial, e.g., leuco methylene blue, which is essentially colorless, isoxidized to form an opaque or semi-opaque layer (e.g., the deep bluedye, methylene blue). Data storage media with the opaque/semi-opaquelayer can no longer be played in media players. By adjusting the time ittakes to turn opaque, this method can be used to provide limited-playdata storage media having the desired life for the given application.

The reactive layer, which comprises both a carrier and a reactivematerial, should initially have sufficient transmission to enable dataretrieval by the data storage media device, and subsequently form alayer which inhibits data retrieval by that device (e.g., which absorbsa sufficient amount of light i.e., incident and/or reflected light) atthe wavelength of the laser in the given device). Typically a layer thatallows an initial percent reflectivity from the reflective layer ofabout 50% or greater can be employed, with an initial percentreflectivity of about 65% or greater preferred, and an initial percentreflection of about 75% or greater more preferred. Once the media hasbeen exposed to oxygen, e.g., air, for a desired period of time (e.g.,the desired allowable play time of the media), the layer preferablycomprises a percent reflectivity of about 45% or less, with about 30% orless preferred, about 20% or less more preferred, and about 15% or lessespecially preferred.

Possible reactive materials include oxygen sensitive leuco or reducedforms of Methylene Blue, Brilliant Cresyl Blue, Basic Blue 3, MethyleneGreen, Taylor's Blue, Meldola's Blue, New Methylene Blue, Thionin, NileBlue, Celestine Blue, and Toluidine 0, as well as reaction products andcombinations comprising at least one of the foregoing material; thestructures of which are set forth below:

Methylene Blue 661 mn

Brilliant Cresyl Blue 622 nm

Toluidine Blue O 626 nm

Basic Blue 3 654 nm

Methylene Green 657, 618 nm

Taylor's Blue 649 nm

Janus Green B 660, 395 nm

Meldola's Blue 570 nm

New Methylene Blue 630, 591 nm

Thionin 598 nm

Nile Blue 638 nm

Celestine Blue 642 nm

A method of synthesis of leucomethylene blue and the oxygen dependentreoxidation to form the colored form of the methylene blue dye is shownbelow:

In addition to the above reactive materials, numerous other dyes andlight blocking materials, can be synthesized to operate to render thedata storage media limited play. For example, some other possiblereactive materials can be found in U.S. Pat. No. 4,404,257, hereafterincorporated by reference, and U.S. Pat. No. 5,815,484, hereafterincorporated by reference. The reactive materials can further comprise amixture comprising at least one of any of the above mentioned reactivematerials.

The reactive material is preferably mixed with a carrier for depositionon and/or impregnation into at least a portion of the surface of thesubstrate. Possible carriers comprise the thermoplastic acrylicpolymers, polyester resins, epoxy resins, polythiolenes, UV curableorganic resins, polyurethanes, thermosettable acrylic polymers, alkyds,vinyl resins and the like, as well as combinations comprising at leastone of the foregoing carriers. Polyesters include, for example thereaction products of aliphatic dicarboxylic acids including, e.g.,fumaric or maleic acid with glycols, such as ethyleneglycol,propyleneglycol, neopentylglycol, and the like, as well as reactionproducts and mixtures comprising at least one of the foregoing.

Some epoxy resins, which can be the used as the organic resin, includemonomeric, dimeric, oligomeric, or polymeric epoxy material containingone or a plurality of epoxy functional groups. For example, reactionproducts of bis phenol-A and epichlorohydrin, or the epichlorohydrinwith phenol-formaldehyde resins, and the like. Other organic resins canbe in the form of mixtures of polyolefin and polythiols, such as shownby Kehr et al, U.S. Pat. Nos. 3,697,395 and 3,697,402, hereafterincorporated by reference.

A Non-Bonding Reactive Layer

Optionally, the reactive layer can be applied to the substrate usingvarious coating techniques such as painting, dipping, spraying, spincoating, screen printing, and the like. For example, the reactive layercan be mixed with a relatively volatile solvent, preferably an organicsolvent, which is substantially inert towards the polycarbonate, i.e.,will not attack and adversely affect the polycarbonate, but which iscapable of dissolving the carrier. Examples of some suitable organicsolvents include ethylene glycol diacetate, butoxyethanol, the loweralkanols, and the like.

For surface coatings, the reactive layer may also optionally containvarious additives such as flatting agents, surface active agents,thixotropic agents, and the like, and reaction products and combinationscomprising at least one of the foregoing additives. The thickness of thereactive layer is dependent upon the particular reactive materialemployed, the concentration thereof in the reactive layer, and thedesired absorption characteristics of the layer both initially and aftera desired period of time.

Development of Blocked Reactive Compounds

One embodiment of the present invention is the use of blocked forms ofthe reactive compounds in the reactive layer. These compounds willunblock within a predetermined time period after the disc ismanufactured or packaged, and typically before the disc is used by theconsumer. This is desirable when the stimulus that triggers the reactionthat causes the disc to become unplayable (e.g., atmospheric oxygen) cantrigger this reaction during the manufacturing of the disc, and thusmeasures need to be taken so that the reactive compound is not activatedduring the manufacturing of the disc. For example, in the case of oxygentriggered reactions, unless a blocked form of the reactive compound isused, manufacturing may need to take place in an oxygen freeenvironment, such as a nitrogen atmosphere.

One embodiment of the present invention comprises the idea of using achemically blocked reactive substance for the purpose of producingoptical discs that become unplayable after being exposed to oxygen, aspecific such blocked leuco dye, a method of preparing this leuco dyeprecursor, a formulation including this leuco dye precursor whichpermits the deblocking and oxidation of the leuco dye precursor atacceptable rates, methods of applying this formulation to optical discsboth on the surface of optical discs and as bonding layers for opticaldiscs, the use of bases to increase the rate of methylene bluegeneration in blocked leuco dye-containing layers in or on opticaldiscs, and the use of silyllaating agents such as hexamethyldisilazaneto stabilize the blocked leuco dye in coating fluids.

In one embodiment of the invention, to manufacture an optical disc thatbecomes unplayable after being removed from its package (a “limited-playdisc”), the disc incorporates a reactive layer with a compositioncontaining a leuco dye which oxidizes to a colored dye which absorbslight at the wavelength of the reading laser of an optical disc player,preventing enough of the reading laser light from being reflected offthe disc to render the disc unplayable. The oxidation of the leuco dyecan be initiated by exposure of the coating containing the dye toatmospheric oxygen, which diffuses through the coating to oxidize theleuco dye molecules. One problem with putting such a coating on thesurface of the disc is the possibility of the coating being removed by aconsumer to make the disc permanently playable. Another problem withputting such a coating on the surface of an optical disc is that thisrequires an additional step in the disc manufacturing process, entailinghigher cost, special tooling for production equipment, and inevitablylower manufacturing yields. Finally, the oxygen-sensitive fluid used tomake such a coating is difficult to handle because of its oxygensensitivity.

In some methods of coating a leuco-dye-containing fluid on the surfaceof an optical disc, some of which were described above, the coating issolvent based and the solvent must evaporate to yield a hard coatcontaining the leuco dye and any other components required, typicallybound in a polymer matrix. There are several disadvantages to such asolvent coating. First, most of the solvent based fluid is spun off ofthe disc during a spin coating manufacturing process and is difficult orimpossible to recover due to solvent evaporation, which both wastesfluid (increasing the cost of the process) and fouls the coatingequipment. Second, evaporation of the solvent takes time, which reducesthe rate at which such coated discs can be manufactured and therebyincreases the cost of the process. Third, the solvent vapors emitted bythe coated disc during the coating and drying process must be ventedfrom the manufacturing equipment, increasing the cost of the installedequipment and presenting process and environmental obstacles to discreplicators considering adopting this manufacturing process.

All of the problems discussed in the previous two paragraphs could beavoided if the leuco dye could be coated in a solventless, light orradiation cured (hereafter called generically “UV-cured”) layer, and ifthis layer could be the same as the optical disc bonding layer that isused to bond the two substrates which compose certain types of opticaldisc, such as a DVD. The major obstacle to creating such a system isthat many leuco dyes, and in particular leucomethylene blue (hereafter“LMB”, which has been used by the present inventors to render DVDsunplayable in a solvent-based, surface coated system), inhibit bothradical and cationic polymerization reactions of the type used to cureUV-curable monomers such as the acrylates that are commonly used asadhesives for bonding DVD substrates. The oxidized dyes (includingmethylene blue) also are inhibitors of such polymerization reactions. Soputting a leuco dye (which will inevitably contain some of the oxidized,colored dye) in a UV-curable composition will either prevent theUV-curing from taking place, or slow the UV-curing and make the processmuch less economical by reducing the rate at which discs can bemanufactured. Moreover, the process of UV-curing can result in some ofthe leuco dye becoming oxidized if any oxygen or other oxidizing agentis present in the layer to be cured, resulting in a product prematurelycontaining oxidized dye which may interfere with the readability of thedisc or change the rate at which it becomes unreadable after exposure tooxygen.

Chemically blocked (sometimes called “protected”) leuco dyes (alsocalled “leuco dye precursors”) are known and have been used for decadesin applications such as “carbonless copy paper”. In particular, blockedversions of leucomethylene blue are known and have been used in suchapplications, and one such compound at least, benzoyl-leucomethyleneblue (BLMB), is commercially available. However, we have found that BLMBdoes not deblock easily enough to yield an acceptable limited play DVDproduct. Other blocked leucomethylene blue compounds share this problem,or deblock too easily such that oxidizable leucomethylene blue isgenerated in the coating fluid before it is desired.

We have found that triisopropylsilyloxycarbonylleucomethylene blue(hereafter “TIPSOCLMB”), whose structure and exemplary synthesis areillustrated in FIG. 17 and described in Example 4, has the followingdesirable properties for use in creating limited-play DVDs:

-   -   1. It is readily synthesized in two steps from commercially        available starting materials. By isolating and purifying the        BOC-LMB produced in the first step as shown in FIG. 17, the        TIPSOCLMB is prepared from a pure compound rather than from the        typically very impure methylene blue.    -   2. It can be incorporated into an acrylate formulation described        in Example 5 in which it is stable (to conversion to oxidized,        methylene blue) for at least several weeks at temperatures below        0 C, allowing coating formulations to be prepared at one        facility and shipped to another facility for DVD manufacturing        if desired.    -   3. It can be deblocked in a period of a week or less, presumably        by a hydrolysis reaction involving water or other nucleophiles        which can either be provided in the acrylate formulation or be        absorbed from the atmosphere in which the DVD is manufactured or        in the DVD packaging material.    -   4. The deblocked LMB is stable (to oxidation to methylene blue)        in the absence of oxygen. The rate at which the deblocked LMB        oxidizes in the presence of oxygen can be controlled by        controlling the effective pH of the coating formulation. It is        known in the art that the rate of oxidation of LMB increases as        the pH of its environment increases. Thus the rate of oxidation        can be increased by the addition of basic substances that are        soluble in the matrix containing deblocked or blocked LMB and        which do not react with the matrix or substrate used. One such        basic compound is DABCO (1,4-diazabicyclo[2.2.2]octane), an        amine. Other amines may be added or substituted. Further, the        addition of a strong protic acid such as camphorsulfonic acid        decreases the rate of LMB oxidation in a polymer film.    -   5. In the absence of water or other nucleophiles, it is a stable        solid which can be stored after synthesis for at least several        months, even in the presence of oxygen. Acrylate-based coating        fluids containing TIPSOCLMB can be handled in the presence of        oxygen until the deblocking reaction has taken place, which        reaction is slow enough that the handling of the coating fluid        during the DVD manufacturing process can be done in normal        (undried) air and is not difficult.

EXAMPLE 3 BocLMB Preparation

Chemical Amount Moles Mol. Wt. Na₂S₂O₄ 60.0 g 0.345 (2.1 eq) 174.11 H₂O 300 mL 10% aq. NaOH  240 mL Methylene Blue 60.0 g 0.160 373.90 CH₂Cl₂ 700 mL + 25 mL Boc₂O   81 mL (d = 0.95 g/mL) 0.352 (2.2 eq) 218.25 DMAP 3.0 g 0.025 (0.15 eq) 122.17 Hexanes  400 mL Methanol  200 mL estimate

In a 2-liter separatory funnel was dissolved 60.0 g of sodiumhydrosulfite (sodium dithionite, Na₂S₂O₄) in 300 mL cold distilledwater. To this solution was added 60.0 g methylene blue (dark greenpowder) from several different bottles, and the separatory funnel wasstoppered and shaken vigorously over a 30-minute period, during whichtime the dark green solids gradually form a tan suspension of insolubleleucomethylene blue. To this suspension was added three 60-mL portionsof 10% aqueous sodium hydroxide solution with vigorous shaking aftereach addition. Some heat is evolved, and a lighter suspension results.After allowing the mixture to stand for a short while to cool, 700 mLmethylene chloride was added and the separatory funnel was stoppered andshaken to dissolve the solids. An amber organic layer began to separatebelow an emulsion. An additional portion of 60 mL aqueous NaOH wasadded, the stoppered funnel was shaken, and the emulsion was allowed tostand for 30–60 minutes to separate into two liquid phases.Alternatively, fresh Na₂S₂O₄ and reasonably pure methylene blue may beused to result in a faster and cleaner phase separation.

To a 1-liter, 3-necked, round-bottomed flask equipped with a magneticstirrer and nitrogen inlet inside a fluted adapter (Aldrich Z11,563-0)packed with 1.5 sheets of crumpled small Kimwipe® tissues (11×21 cm) wasadded 81.0 mL di-tert-butyldicarbonate (Boc₂O) diluted with 25 mLmethylene chloride. After stirring under nitrogen for 5–10 minutes, 3.0g of 4-(dimethylamino)pyridine (DMAP) was added followed by dropwiseaddition of the leucomethylene blue solution from the separatory funneland through the fluted Kimwipe-containing tube. The stem of theseparatory funnel was connected to the fluted tube through a one-holedrubber stopper so that the addition was performed under nitrogen. Gasevolution (CO₂) began immediately. After two hours, the addition wascompleted to give a dusty green reaction mixture that was stirredovernight under nitrogen at room temperature.

On the following morning, the dusty green reaction mixture was arrangedfor atmospheric distillation. About 550 mL CH₂Cl₂ was distilled off andreplaced with 300 mL hexanes. A gray-blue solid separated out.Distillation was continued until the head temperature reached about 55°C. The mixture was allowed to cool; then the solid was collected byfiltration through a sintered glass funnel. The solid was washed withhexanes (2×50 mL) to remove excess Boc₂O, and then it was washed withmethanol (amount unspecified, 4×50 mL estimate) to remove unreacted andoxidized leucomethylene blue until the wash liquid was only faintlyblue. The resulting gray solid was dried in air and then under vacuum atroom temperature. Yield: 47.0 g (76%). (MW of BocLMB=385.53)

Thin layer chromatography analysis on a 5×10 cm Whatman K5F silica gelplate eluting with 5% acetone in methylene chloride showed a faint bluespot at the origin, a very weak spot at R_(f)=0.58, and a large productspot at R_(f)=0.63. The initially colorless product spot became darkblue upon standing in air, and rapidly when heated in a 120° C. oven.

Repetition of this reaction at the same scale resulted in a yield of48.0 g (78%).

EXAMPLE 4 TipsocLMB Preparation

Chemical Amount Moles Mol. Wt. BocLMB 35.61 g 0.092 385.53 CH₂Cl₂   200mL 2,6-Lutidine  26.0 mL (d = 0.92 g/mL) 0.223 (2.5 eq) 107.16 TipsOTf 39.0 mL (d = 1.14 g/mL) 0.145 (1.5 eq) 306.42 Hexanes   420 mL

To a 500-mL, 3-necked, round-bottomed flask equipped with a magneticstirrer, addition funnel, and condenser under a nitrogen bubbler wasdissolved 35.61 g BocLMB in 200 mL methylene chloride to give a bluesolution. To this solution was added 26.0 mL 2,6-lutidine followed bydropwise addition of 39.0 mL of triisopropylsilyltrifluoromethanesulfonate (TipsOTf) over a 15 minute time period. Thegreen-blue reaction mixture was then stirred under reflux for 6 hours.TLC analysis (K5F silica, 5% acetone/CH₂Cl₂) showed only a small amountof BocLMB starting material present at R_(f)=0.67 with a large productspot at R_(f)=0.74. The reaction mixture was then stirred overnight atroom temperature under nitrogen.

On the next morning, the green-blue clear reaction mixture was againstirred under reflux for one hour. TLC analysis still indicated that atrace of BocLMB or similar R_(f) impurity was present. The solution wasthen concentrated on a rotary evaporator under vacuum to remove most ofthe methylene chloride, resulting in a dark green-blue syrup. Afteraddition of 200 mL hexanes, the mixture was stirred by hand to effectthe separation of a blue-gray solid. Upon heating this mixture underreflux with continued hand stirring, the TipsocLMB product dissolved inthe hot hexanes leaving behind a dark blue salt residue as a melt orcrusty solid. The hot hexanes solution was decanted from the residue,and the residue was further extracted with 60 mL boiling hexanes. Thecombined hot hexanes extract (green in color) was allowed to coolslightly and was then filtered through a 1.5 cm-thick layer of Celite toobtain a clear, pale tan filtrate. After washing the Celite twice with30 mL portions of hot hexanes, the combined filtrate (˜320 mL volume)was placed in the freezer (about −20° C.) overnight.

On the following morning, an off-white solid with a greenish cast wasobserved to have crystallized. The mixture was filtered cold, and theproduct was washed with cold hexanes (2×50 mL), sucked dry, and driedunder vacuum at room temperature to an off-white solid. Yield: 33.3 g(75%). (MW of TipsocLMB=485.77) The melting point from an earlier runwas 121–123° C.

TLC analysis (K5F silica, 3% acetone/CH₂Cl₂) showed very weak spots atthe origin and at R_(f)=0.53 (probably unreactied BocLMB) with the mainspot at R_(f)=0.61 that is initially colorless and becomes dark blueupon standing at room temperature for several hours, or in a 120° C.oven for a few minutes.

Examples 5 and 6 illustrate how TIPSOCLMB can be incorporated in acoating fluid that can be UV-cured to create a reactive layer containingTIPSOCLMB. Example 7 illustrates how the above technique can produce aninterstitial reactive layer, which allows the Special DVD-5 designs 1, 2and 3 to be used to manufacture expiring optical discs. Example 8illustrates how TIPSOCLMB deblocks and becomes oxygen sensitive LMB ineither a surface or an interstitial layer. When exposed to oxygen, theLMB oxidizes into methylene blue, as illustrated by the increasing cyandensity in FIG. 18; methylene blue strongly absorbs light in the 650 nmwavelength, as illustrated in FIG. 19.

EXAMPLE 5 Formulation of Coating Fluid Containing TIPSOCLMB

-   80 mg TIPSOCLMB-   80 mg Irgacure 819 (Ciba Geigy; sensitizer)-   40 ml CD-501 acrylate (Sartomer;    propoxylated[6]trinmethylolpropanetriacrylate)-   18.5 mg 1,4-diazabicyclo[2.2.2]octane (“Dabco”; Aldrich; base)-   155 μl 1,1,1,3,3,3-hexamethyldisilazane (“HMDZ”; Aldrich”;    stabilizer)

The TIPSOCLMB, Irgacure 819, and Dabco are weighed into a brown glassbottle, a stir bar is added, the CD-501 is poured in to the properweight, and the HMDZ is added by syringe. Dry nitrogen is blown into thebottle for a few minutes and the bottle is capped and the cap covered byparafilm. The contents are stirred at room temperature for at least twohours to dissolve the solids. If not all of the material is used, blowthe bottle with nitrogen, cap and seal with parafilm, and store in afreezer; warm the bottle before opening to prevent water from condensingin the bottle.

EXAMPLE 6 Preparation of Disk Surface-coated with TIPSOCLMB/acrylateFormulation

A DVD clear half disk (an unmetalized 0.6 mm thick and 120 mm diameterpolycarbonate disc) or a full DVD (two layers bonded together, back toback with a adhesive) is centered on a laboratory spin coating turntablerotating at roughly 60 rpm's. A 4 ml solution from example #5 is thenapplied uniformly in a circular ring by a syringe at about a 34 to 40 mmdiameter from the center of the disc. The spin speed is then rapidlyincreased to about 200 rpm for about 15 seconds, resulting in a coatingof acrylate/TIPSOCLMB fluid about five Am thick. The spinning is slowed;excess fluid wiped off of the edge of the disk with a tissue and basesolvent, if available, and then removed to a lab bench. At this point,the disc is subjected to about five flashes from a Norlite 400 xenonflash lamp at its max setting. The time between flashes is dictated bythe charging of the flash lamp, but should be sufficient as to notinduce added stress from heat generated in the cure (typically about 5seconds). This process will yield a clear, uncolored, fully curedacrylate film. Other disks are also prepared with similar acrylateformulations that contain either no Dabco or 10× the amount of Dabcodescribed in Example 5.

EXAMPLE 7 Preparation of Disk Sandwich-coated with TIPSOCLMB/acrylateFormulation

A DVD half disk is centered data side up on the turntable as statedabove. The turntable is held stationary while the fluid is dispensed onthe data side in a manner creating drops with a syringe roughly 3˜5 mmround. These are evenly spaced about 3 mm apart on a diameter of 30˜40mm. The disc to be bonded is then placed data side facing the solutionand slightly bowed away from the bottom disc by the edges. The disc willbe lowered at an angle until the first contact point between a fluiddrop and top disc occurs. We do not want to place the top discimmediately on the bottom because of entrapped air and subsequentbubbles. Therefore, to get a more uniform capillary flow, we can rotatethe disc in a clockwise rotation while keeping it slightly bent underlight pressure until each of the fluid drops begins to form a capillarybridge ring. Once the capillary ring is completed, the top disc can bereleased and the capillary action will continue. We can wait for thecapillary flow to cover the surface, or we can spin the disc at 100rpm's until the material at least reaches the maximum OD diameter. Atthis point the turntable can be turned on and rotated at about 500 rpm'sfor 5 seconds. This will level the spacer layer (adhesive layer) andremove excess material from the OD. The disc edge can then be wiped andthe disc will then be UV cured. It is important that prior to curing,the disc halves be aligned as close as possible to avoid center holemisalignment an subsequent play back problems. At this point, the discis subjected to about 20˜30 flashes from a Norlite 400 xenon flash lampat its max setting. The time between flashes is dictated by the chargingof the flash lamp, but should be sufficient as to not induce addedstress from heat generated in the cure (Typically 5 seconds). Thisprocess will yield a clear, uncolored, fully cured acrylate film. Otherdisks are prepared with similar acrylate formulations that containeither no Dabco or 10× the amount of Dabco described in Example 5.

EXAMPLE 8 Deblocking and Oxidation of TIPSOCLMB in Surface andSandwich-coated Disks, and the Effect of a Base Included in the CoatingFormulation

Disks prepared as described in Examples 6 and 7 were cut into six‘chips’ each and the chips were stored in either dry nitrogen, dry air,or room air (average RH about 30%) and their cyan reflectance densitieswere recorded periodically with an X-Rite 504 densitometer (the samplesstored in nitrogen were only tested at the start and end of theexperiment as they were visibly unchanged and it was desired to minimizetheir exposure to oxygen). In all cases the samples stored in nitrogenshowed no methylene blue (MB) generation, as expected. Incorporating1,4-diazabicyclo[2.2.2]octane (Dabco) into an acrylate formulation at1.0 equivalent with respect to the TIPSOCLMB gave very significantacceleration of the deblocking/oxidation rate compared to a control(FIG. 18), while a higher concentration of this compound was actuallyless effective. In general the open samples (those with the TIPSOCLMBlayer coated on top of a DVD half without any cover) generated MB onlyslightly faster than the sandwich structures, indicating that deblockingand oxidation of the LMB is not significantly limited by the transfer ofeither water or oxygen through an unmetallized 0.6 mm polycarbonatelayer. Rather, the deblocking of the TIPSOCLMB is likely to berate-limiting in these systems. The control samples without any addedbase shows noticeably faster MB generation in room air than in dry air,suggesting that moisture in the air speeds deblocking in this sample.

Example 9 illustrates how a reactive bonding layer was incorporated intoSpecial DVD-5 Design #2, thus manufacturing a disc that was normallyplayable like a DVD-5 and subsequently became unplayable.

EXAMPLE 9 Incorporating TIPSOCLMB into a Special DVD-5 Design #2 BondingLayer

A set of experiments was performed to test whether a formulationcontaining TIPSOCLMB, Irgacure-819, Dabco,1,1,1,3,3,3-hexamethyldisilazane (as a fluid stabilizer), and SartomerCD-501 acrylate monomer could be used as a DVD adhesive to produceplayable DVDs. Using the formulation described in Example 5, filteredthrough a 1.0 μm glass syringe filter, the fluid was syringed ontoeither clear or metallized Special DVD-5 Design #2 halves manufacturedas in Example 2. A DVD half disk is centered data side up on theturntable as stated above. The turntable is held stationary while thefluid is dispensed on the data side in a manner by creating drops with asyringe roughly 3˜5 mm round. These are evenly spaced circularly about adiameter of 30˜40 mm. The disc to be bonded is then placed data sidefacing the solution and slightly bowed away from the bottom disc by theedges. The disc will be lowered at an angle until the first contactpoint between the fluid and top disc occurs. We do not want to place thetop disc immediately on the bottom because of entrapped air andsubsequent bubbles. Therefore, to get a more uniform capillary flow, wecan rotate the disc in a clockwise rotation while keeping it slightlybent under light pressure until each of the fluid drops begins to form acapillary bridge ring. Once the capillary ring is completed, the topdisc can be released and the capillary action will continue. We can waitfor the capillary flow to cover the surface, or we can spin the disc at100 rpm until the material reaches the maximum OD diameter. At thispoint the turntable can be turned up and rotated at about 500 rpm's for5 seconds to thin out the adhesive and achieve a resulting 50 μmadhesive films (determined by profilometry). This will level the spacerlayer (adhesive layer) and remove excess material from the OD. The discedge can then be wiped and then the disc UV cured. It is important thatprior to curing, the disc halves be aligned as close as possible toavoid center hole misalignment an subsequent play back problems. At thispoint, the disc is subjected to about 20˜30 flashes from a Norlite 400xenon flash lamp at its max setting. The time between flashes isdictated by the charging of the flash lamp, but should be sufficient asto not induce added stress from heat generated in the cure (Typically 5seconds). This process will yield a clear, uncolored, fully curedacrylate film that plays on the DVD test player.

The discs were manufactured under normal ambient conditions, and weresubsequently put in a nitrogen box for 34 days, to remove the oxygendissolved in the substrates (which would take an estimated 12-20 hours),and to allow TIPSOCLMB to unblock into LMB (which would take 2–3 days).

The Special DVD-5 design #2 discs were subsequently removed from thenitrogen box and were measured for reflectivity at the 650 nm wavelengthas a function of time. The discs were clear and playable for 12–16 hoursafter which time they turned dark blue within 24 hours and becameunplayable with reflectivities under 2% at 650 nm.

Multiple-layer Optical Discs

As seen in the DVD family illustration in FIG. 4, in a dual layeroptical disc designed to read multiple layers from one side, the spacer(bonding) layer is in the optical path. In the case of Dual Layer DVDs,the given specification for this spacer layer thickness is 0.055+/−0.015mm. The thickness of the substrate for a dual layer DVD with opticalpath bonding is typically 055 mm˜0.64 mm.

Incorporating a reactive compound inhibiting the reading laser in thebonding layer 800 of either type of dual-layer disc would only inhibitthe player from reading the L1 layer 805, as the bonding layer 800 isnot in the optical path for reading the L0 layer 810. Furthermore, themetal 815 in the L0 layer 810 might act as a barrier preventing apredetermined stimulus such as moisture or oxygen to permeate to thereactive compound in the bonding layer 800 in a controllable manner.

One method around this potential problem would be as follows. Typically,when a player or a drive begins reading a disc, it looks for the tableof contents or information area in the lead-in area for the L0 layer 810(see FIG. 6). When authoring the disc, it is possible to have the L0lead-in 820 area contain commands to directly access the L1 layer 805.In order to be able to read the L0 layer 810 to direct the play sequenceto the L1 805, we would have to metallize the L0 side 810. This wouldthen possibly interfere with the reactive adhesive material 800 causingunstable or uncontrolled kinetics of reaction that would be dependent onthe permeability of the metal layer. One approach around this would beto change the metallizer masking for the L0 semi-reflective layer 800,which is typically run out to 58 mm to 59 mm radius on the disc, tosomething closer to the lead-in or information data area on the L0.

To facilitate activation of the reactive material 800, e.g., when theactivating stimulus is oxygen or moisture that might be prevented fromreaching the reactive bonding layer 800 because of the L0 metal layer820, part of the L0 layer 810 can be masked during metallization, sothat part of the reactive layer will be easier to expose to the stimulusand thus the corresponding part of the L0 layer will be disabled. Thesediscs would have a partially metallized L0 layer 810, as illustrated inFIG. 20. For example, if only the lead-in area or program start portionof the L0 layer 810 is metallized, the player is able to read thelead-in data, and is able to access the information stored on L1 layer805. As only a small area on the L0 layer 810 would be metallized, asubstantial part of the reactive bonding layer would be in directcontact with the L0 substrate 810, which is typically permeable bystimuli such as oxygen or moisture. When the reactive bonding layerresponds to the appropriate stimuli and starts interfering with thereading laser, the player is no longer able to access the correspondingpart of the L1 layer 805.

Another embodiment of the present invention is utilizing authoringtechniques, such as sequencing and branching commands to be executed bythe optical media player, to ensure that making a certain part of a discunplayable will interfere with playing other parts of the disc, or theentire disc. The part of the disc made unplayable for this purpose maybe in the single layer of a one-layer disc, or in any of the layers of amulti-layer disc. For example, one embodiment of this invention consistsof a DVD-9 authored so that making a certain part of the L1 layerunplayable would interfere with playing other parts of the disc, or theentirety of the disc. For example, reading the L0 layer lead-in areawould direct the player to access a part of the L1 layer that wouldbecome unreadable when the reactive layer starts interfering with thereading laser, which would cause the disc to be inoperable. A DVD-9 disccan be authored so that all or part of the L1 layer is essential inorder to play any information on L0 and/or L1. For example each chapteron the disc can be authored so that it requires reading certaininformation on L1 before proceeding.

In another embodiment of this invention, activation of the reactivematerial is facilitated by controlling the deposition of the L0 layer.For example, fast deposition of a gold or silver or silicon L0 layerthrough sputtering is known to result in grainy dendritic formationsthat are easier to penetrate by oxygen and moisture. Also, a thinner L0layer can be deposited, which is easier to penetrate by oxygen andmoisture. While depositing grainy or thin L0 layers may be unacceptablefor a permanent, archival quality disc, it is often adequate for alimited use, expiring disc.

EXAMPLE 10 DVD-9 Discs with TIPSOCLMB Incorporated in a Reactive BondingLayer

A DVD-9 with parallel track path encoding can have two distinctlydifferent layers for play back. In the encoding or data masteringprocess, the Lead-in area normally found on the L0 disc, can haveinformation telling the reading players to read from either or bothlayers on the disc. Therefore, for this example using a reactive bondingmaterial, the reactive layer could prevent play back from the L1 layerwhile not affecting the L0. For this example corresponding L0 and L1masters were manufactured, and L0 and L1 substrates were normally moldedand metallized.

The DVD halves were bonded as in example 9 above using an adhesivecontaining the formulation TIPSOCLMB, Irgacure-819, Dabco,1,1,1,3,3,3-hexamethyldisilazane (as a fluid stabilizer), and SartomerCD-501 acrylate monomer described in Example 5. The solution wasfiltered through a 1.0-μm glass syringe filter. A DVD half disk iscentered data side up on the turntable as stated above. The turntable isheld stationary while the fluid is dispensed on the data side in amanner by creating drops with a syringe roughly 3˜5 mm round. These armevenly spaced circularly about a diameter of 30˜40 mm. The disc to bebonded is then placed data side facing the solution and slightly bowedaway from the bottom disc by the edges. The disc will be lowered at anangle until the first contact point between the fluid and top discoccurs. We do not want to place the top disc immediately on the bottombecause of entrapped air and subsequent bubbles. Therefore, to get amore uniform capillary flow, we can rotate the disc in a clockwiserotation while keeping it slightly bent under light pressure until eachof the fluid drops begins to form a capillary bridge ring. Once thecapillary ring is completed, the top disc can be released and thecapillary action will continue. We can wait for the capillary flow tocover the surface, or we can spin the disc at 100 rpm until the materialreaches the maximum OD diameter. At this point the turntable can beturned up and rotated at about 500 rpm's for 5 seconds to thin out theadhesive and achieve a resulting 50 μm adhesive films (determined byprofilometry). This will level the spacer layer (adhesive layer) andremove excess material from the OD. The disc edge can then be wiped andthen the disc UV cured. It is important that prior to curing, the dischalves be aligned as close as possible to avoid center hole misalignmentan subsequent play back problems. At this point, the disc is subjectedto about 20˜30 flashes from a Norlite 400 xenon flash lamp at its maxsetting. The time between flashes is dictated by the charging of theflash lamp, but should be sufficient as to not induce added stress fromheat generated in the cure (Typically 5 seconds). This process willyield a clear, uncolored, fully cured acrylate film that plays on theDVD test player.

The discs were manufactured under normal ambient conditions, and weresubsequently put in a nitrogen box for 7 days, to remove the oxygendissolved in the substrates (which would take an estimated 12–20 hours),and to allow TIPSOCLMB to unblock into LMB (which was estimated to takeup to 5–6 days). The discs were subsequently removed from the nitrogenbox and were normally playable on both the L0 and L1 layer for 2–3 dayson a Pioneer player. After 7 days of exposure to ambient oxygen, thediscs became unplayable on the L1 layer, although they would playnormally on the L0 layer.

EXAMPLE 11 DVD-9 Discs with Partially Metallized L0 Layer

As in example 10 above, DVD-9 master tapes were generated with the dataarea being identified on layer L1 and the L0 layer serving only toprovide the lead-in and subsequent table of contents relating to thedisc type and information. During play back, the L0 lead-in wouldinstruct the disc to read from the L1 data side. In this case, we wouldnot have to metalize the entire surface of the L0 layer because there isno information to be read outside of the lead-in area. Therefore, DVD-9master tapes were produced with lead-in and command information on L0and data area on L1. Typically, the metalizer masking covers areas from25 mm through 118 mm diameters on both layers. Being as the lead-in areadata covers the diameters of 25.2 mm to a maximum of 48 mm, and thesubsequent information area starts at no less than 48 mm diameter, themetalizer masking can be reduced to cover the lead-in only. This wouldallow a reflective signal to read the lead-in on the L0 layer and thenswitch to the L1 layer for data playback without having to read throughadditional semi-reflective metal.

In this example, we manufactured donut-masking plates that dropped intothe metalizer OD mask assembly. By registering the masking from the OD,we are able to reduce the metalized diameter to an area allowing lead-inplayback. We extended the mask just outside of the lead-in 48 mmdiameter in order to compensate for eccentricity tolerance with themasking position. Additionally, in order to prevent a reflective spikefrom the transition of clear disc area to metalized disc area whenreading the L1 layer, the edge of the masking was slightly raised abovethe disc to cause a shadowing or tapered layer uniformity. This wouldcause a gradual focusing compensation rather than a large “speed bump”effect causing its radial noise and focusing error to fall out ofspecification and perhaps jump track.

The resulting DVD-9 halves were bonded as in Example 10. The DVD-9sconstructed were tested for playability in a Pioneer DVD player and in aDVD-ROM drive, and were subsequently put in a nitrogen box for 7 days,so that the TIPSOCLMB would unblock into LMB. The discs weresubsequently removed from the nitrogen box and were clear and playablefor 12–16 hours, and turned dark blue within 24 hours after that,becoming unplayable. The discs were effectively prevented from havinginformation read from either L0 or L1.

Controlling the Timing of the Reaction

Preferably, the data quality of the disc should remain high for theintended period of use and then decay rapidly resulting in a rapiddegradation of the ability to read data off the optical disc. Onebenefit of this embodiment of the present invention is that for a broadclass of stimuli, such as those requiring diffusion of a substancethrough a barrier layer, incorporating the reactive material in aninterstitial layer results in substantial advantages regarding thetiming characteristics of the reaction.

One method of achieving the above mentioned desirable timingcharacteristics is to use a reactive interstitial material between thedisc substrates, as described earlier, which reacts with a substancethat needs to diffuse through the substrates of the disc. For example,if the reactive material is sensitive to oxygen, there will be anextended period in which there will be no reaction while the oxygendiffuses through the disc substrates. Once oxygen reaches the reactivelayer, the resulting reaction can be fast, resulting in rapid expirationof the disc.

When oxygen is used as the diffusing substance, it may be necessary toremove oxygen that dissolves in the disc during the different stages ofits manufacture. This can be done, for example, by storing the discs ina vacuum or in an oxygen free environment for an appropriate period oftime. It has been established theoretically and experimentally that 24hours is an adequate period to extricate oxygen dissolved in a 0.6 mmthick polycarbonate disc substrate. Alternatively, if a blocked reactivematerial is used as described earlier, an oxygen scavenging material,such as iron or an organometallic compound, can be used to extricateoxygen from the optical disc before the blocked reactive materialunblocks. This method has several manufacturing advantages; for example,it can avoid oxygen extrication during manufacturing of the disc byincluding the oxygen scavenging material in the packaging of the disc,which allows the extrication of the oxygen to take place after the discis manufactured and packaged.

Another means for controlling the timing of the expiration of the discis to include in or adjacent to the reactive layer a finite, controlledquantity of an appropriate protective substance, such as an antioxidantin the case that the reactive layer reacts with oxygen. The protectivesubstance would prevent the reactions that cause the disc to expireuntil such time as the anti-oxidant was consumed, at which time the discwould rapidly degrade and become unplayable. For example, anorganometallic compound that reacts with oxygen can be packaged with thedisc to protect the disc from oxidation while in the package.Alternatively, the organometallic compound can be incorporated into thesubstrate, thus continuing to protect the metal layer for a period oftime after the package has been opened.

Depletion of a protective substance could be combined with diffusion ofthe triggering substance through the substrate of the disc, to result inlonger delays before the disc expires, or to enable finer control of thecharacteristics of the expiration process, such as the steepness ofreflectivity degradation.

Example of Antioxidant in Reactive Layer

Alternatively, the protective substance may be a reducing agent whichmay be incorporated into the reactive bonding layer itself. In anexperiment in which the concentration of TLMB was also varied and shownto have an effect, the play time was shown to be more greatly affectedby varying the amount of stannous ethylhexanoate reducing agent (seeTable I).

TABLE I Concentration Play Time (hrs) Formulation # TLMB Sn(II)EtHexanoate short long A   1% 2% 14 22 B   1% 4% 38 55 C 0.5% 2% 18 26 D0.5% 4% 46 58

DVD-5 discs were made using a TIPSOCLMB-containing adhesive formulation,and deblocked in an oxygen-free atmosphere for 48 hours at 60° C. Atthat time the discs were exposed to ambient room air and the rate ofmethylene blue color development was quantified with an X-Ritereflection densitometer. The short Play Time was chosen to be the timeat which the cyan density increased by 0.35, which roughly correspondsto a playability cutoff at 45% reflectance as typified by a low qualityDVD player. The long Play Time was chosen to be the time at which thecyan density increased by 0.85, which roughly corresponds to aplayability cutoff at 10% reflectance as typified by a high quality DVDplayer.

The most likely mechanism for this extended play is reduction of theinitially formed methylene blue dye back to the leuco form until most ofthe reducing agent is consumed. Alternate mechanisms, such as thestannous compound acting as a primary oxygen scavenger to consume oxygenbefore the leuco dye is affected, are also possible.

The mobility within the cured matrix is expected to have a significanteffect upon the reduction rate; indeed, the calculated glass transitiontemperature (Tg) of the monomers used in this example is −34° C. In sucha soft matrix, adequate molecular mobility should exist to allowmolecular contact of reducing agent and dye molecules.

Alternate reducing agents might include other Sn(II) compounds whichwould be soluble in the UV cure formulation, such as acetylacetonatechelates, fatty alpha-aminoacid chelates and salts; soluble iron(II)compounds, such as fatty carboxylates and chelates such asacetylacetonates; ascorbic acid and its derivatives such as ascorbylpalmitate; hydroquinones, such as 2,5-di-tert-amylhydroquinone;alkylhydroxylamines; hydrazines; dithionates with a solubilizingcounterion; reducing saccharides such as glucose; alpha-hydroxyketones,such as acetol; appropriately substituted boron and silicon hydrides.Although many of these materials are difficultly soluble in currentactive adhesive formulations, a more expeditious choice of monomers andoligimers might allow the use of one of these alternate reducing agentswhile still providing good adhesive and dye stabilization properties.

Preventing Expired Discs from Playing in Future Generation Players.

Future generations of optical discs and players are typically developedto offer increased performance for consumers and other users of thetechnology. For example, DVDs offer increased storage capacity comparedto CDs, and the next generation of “blue laser” DVDs will offer improvedcapacity compared to today's DVDs. Subsequent generations of opticalstorage media, such as the “DVR” format currently under development,will have even greater capacity and performance.

Optical media players are typically engineered with the ability to playprevious generations of discs. For example, while CD players employ alaser with a wavelength of 780 nanometers to read CDs, DVD playerstypically employ their reading laser with a wavelength of 650 nanometersto read CD discs. The next generation DVDs (“blue laser DVDs”) isdesigned to be read with a laser with a wavelength of 450–460nanometers; the “DVR” format will use lasers emitting around 405 nm.Future generation players are likely to be able to read current DVDswith their 450–460 nanometer or 405 nanometer lasers.

Dyes used to inhibit the reading laser in current optical disc playersare typically designed to interfere with the reading laser employed bythese players; such dyes, however, may not interfere with the readinglaser future players, which is likely to have a shorter wavelength. Theimplication is that expired discs, even though they may not play in thecurrent generation of players, they may become playable when futuregeneration players become available. Dyes used to inhibit the readinglaser in current DVD players are typically designed to interfere with a650 nanometer reading laser; such dyes, however, may not interfere witha reading laser in the 450–460 nanometer range. For example, methyleneblue, which is one of the read inhibit dyes proposed in Smith et al,while strongly absorbent in the 650 nanometer wavelength, it isessentially transparent in the 450–460 nanometer range (see FIG. 19).The implication is that expired DVDs may play in blue laser DVD players.

Another embodiment of the present invention is an optical disc that willnot play in future generation players, thus preventing an expired discfrom becoming playable when future generation players (e.g., blue laserDVD players) become available. This can be accomplished by incorporatingin the optical path of the disc a selectively interfering layer thatwill interfere with the reading laser of future generation players, andthus will inhibit reading of the disc in such players. Such a layer canbe designed by incorporating a dye or pigment that does not interferewith the reading laser in a certain type of players, but does interferewith the reading laser in other types of players (or will change tobecome interfering in response to a predetermined stimulus). Forexample, Acridine Yellow [135-49-9], is essentially transparent at the635–650 nanometer wavelength but strongly absorbs at the 450–460 and 405nanometer wavelengths (absorption max in ethanol at 462 nm, molarabsorptivity=37,000 M⁻¹cm⁻¹). Alternatively9,10-bis(phenylethynyl)anthracene [10075-85-1] also does not absorb atall in the 635–650 nanometer range, but is strongly absorbent in the450–460 and 405 nanometer range (absorbance max 455 nm in cyclohexane,molar absorptivity 33,000 M⁻¹cm⁻¹). Other classes of dyes and pigmentsthat can be used for blocking blue laser light (at either 450–460 or 405nm) include aromatic hydrocarbons, azo dyes, cyanines, polymethines,carotinoids, hemicyanines, styryls, quinaldines, coumarins, di- andtriarylmethines, anthraquinones, nitro and nitrosos. As mentioned above,methylene blue is essentially transparent at the 450–460 nanometerwavelengths, but strongly absorbs at the 635–650 nanometer range.

In one embodiment of the current invention, the selectively interferinglayer is a dedicated layer in the optical path of the reading laser. Inanother embodiment, which is likely to be the preferred embodimentbecause it does not introduce an additional design element for theoptical disc, the selectively interfering layer is combined with anotherelement of the disc, such as the substrate or the reactive layer. Forexample, this could be accomplished by mixing an appropriate dye orpigment, such as Acridine Yellow [135-49-9] or9,10-bis(phenylethynyl)anthracene [10075-85-1], with the polycarbonateor other polymer used to mold the substrate of the disc, or with thereactive layer in an expiring disc, such as the bonding layer in thespecial DVD-5 designs described earlier.

Use of Additional Mechanisms to Prevent Recovery of Data

Another embodiment of the present invention is combining themechanism(s) that prevent reading of the optical disc by inhibiting thereading laser with additional mechanism(s) for preventing recovery ofthe information encoded in the data structures on the disc. Theseadditional mechanism(s) can be designed with less accurate control ofthe timing of their activation than the mechanism(s) that work byinhibiting the reading laser. Thus it may be desirable to combine themechanism that controls expiration of the optical disc by interferingwith the reading laser with additional mechanism(s) that permanentlyprevent the recovery of the data on the optical disc. For example, adisc may become unplayable by transitioning a layer in the optical pathfrom transparent to opaque in a controlled time period, for exampleapproximately 24 hours after a predetermined stimulus, such as removingthe disc from its packaging. In addition, a secondary mechanism couldcorrode the metal layer on the disc, such mechanism acting over a longerperiod of time, such as 1–2 weeks, and being triggered by the same or adifferent stimulus. Additional mechanisms may also be employed, such asan additive that degrades the polycarbonate material from which the discis composed, which process can be triggered by the same stimulus (suchas exposure to ambient air), or a different stimulus (such as thecentrifugal forces generated when a disc is played in a CD or DVDplayer). Other triggering stimuli for these backup mechanisms caninclude various constituents of air, light, physical motion, and timefrom manufacturing or packaging. Many other mechanisms are possible.

One method of accomplishing this is to deposit a layer of metallicsilver separated from the information bearing aluminum layer by amaterial incorporated for this purpose, or by an existing material, suchas the bonding layer or one of the substrates of the optical disc. Thissilver layer can be above or below the aluminum layer, and if it isbelow (and thus in the optical path of the reading laser) it needs to besufficiently transparent initially so that the reading laser can readthe information on the aluminum layer.

In one embodiment of the invention, a DVD-9 disc is manufactured with areactive bonding layer consisting of a material with appropriatedielectric properties, and with appropriate selection of metals for L0and L1. For example, L0 can be made of silver and L1 can be made ofaluminum.

When a silver layer and an aluminum layer are separated by anappropriate dielectric material, then upon exposure to oxygen the silverserves as a cathode, on which O₂ is reduced, and aluminum serves as ananode. Corrosion is fast only if a short develops between the silver andthe aluminum layers. The development of the short results from thegrowth of a silver dendrite through the separating material. To grow thedendrite through the separating material it is desirable to use amaterial that has some ionic conductivity. Several likely separatingmaterials consist of or contain polyacrylate. If the polyacrylate isslightly hydrolyzed, or if it is, for example, a 2-hydroxyethylacrylatecopolymer, there will be some ionic conductivity. Preferred areco-polymers of poly(acrylonitrile), or of poly(4-vinylpyridine), or ofpoly(1-vinylimdazole). All of these should conduct silver, copper orthallium ions (Ag⁺ Cu⁺ or Tl⁺). Thallium is less preferred due to itstoxicity.

The chemical equations are as follows:

Silver is air-oxidized:4Ag+O₂→Ag₂O (complexed with lacquer)Ag₂O+H₂O+complexant→2Ag⁺ (complexed)+2OH⁻

Ag⁺ is reduced by aluminum, which is oxidized (if Ag⁺ is mobile in thelacquer, which is designed to conduct Ag⁺)Ag⁺+Al→Al³⁺+3Ag⁰Al³⁺+3OH⁻→Al(OH)₃→Al(O)OH+H₂O

A silver dendrite starts growing from the aluminum to the silver. Whenthe two layers are shorted, the “switch” between a battery's (Al) anodeand (Ag) cathode is closed. Corrosion is rapid and catastrophic. Oneskilled in the art will recognize that other similar metals may besubstituted for Al and Ag in this example.

Alternatively, other ways of permanently corroding data layers via thereactive layer can be employed. For example, certain embodiments of thisinvention may have a bonding layer that promotes the corrosion of thereflective metal layer or may involve the diffusion of some substancefrom the bonding layer to the reflective layer(s). In other embodiments,the additional mechanisms will not be part of the bonding material. Forexample, a precursor of a corrosive substance may be deposited adjacentto the metal layer. When oxygen or some other appropriate substancediffuses through the substrate and reaches the corrosive precursor, areaction could be initiated that results in producing a corrosivesubstance that over a period of time permanently destroys the datastructures on the disc. Alternatively, the material in the substrate ofthe disc, such as polycarbonate, could be engineered so that it degradesover a period of time, thus making the disc unusable. Such substancesand reactions are known to the skilled in the art.

Another composition that performs a similar function is one in which thesubstrate itself is modified over time. The modification of thesubstrate could cause it to change its optical qualities, therebydegrading the signal reaching the reader. These optical qualities couldinclude its index of refraction or its transparency.

Moreover, the modification of the substrate could cause the underlyingmetal layer to change its optical properties, as described above. Inthis way, a time-sensitive substrate and/or lacquer could be combinedwith a reflective layer that becomes non-reflective.

The transparency of a polymer film can be changed by any of thefollowing: reaction of the film with water; reaction of the film withoxygen; or crystallization of the polymer, meaning increased alignmentof polymer molecules in the film.

As an example, a substrate could be chosen that is changed by componentsin air such as oxygen or water. For example, oxygen could oxidize thesubstrate, causing a change in its transparency or its index ofrefraction. Alternatively, the substrate could be designed to absorbwater in the air, causing it to swell and change its optical properties.Another example is that the substrate could change its permeability tooxygen over time, thereby permitting the oxidation of the metalliclayer. In the later case, the overall time sensitivity of the opticalmedia could be a function of the properties of both the substrate and/orlacquer and the reflective layer.

The substrate or the metallic layer could also be made sensitive tospecific wavelengths of light. Exposure to these wavelengths would causea change in the optical qualities of the layer, thereby degrading thesignal reaching the reader. Examples include photodepolymerization ofthe substrate; photogeneration of acid; photogeneration of singletoxygen; and unzipping of the polymers (e.g., fissure of cross linkinghydrogen bonds). Incorporation of light-activated catalysts into thesubstrate or the metallic layer can assist in this process.

Accordingly, the present invention has been described at some degree ofparticularity directed to the exemplary embodiments of the presentinvention. It should be appreciated, though, that the present inventionis defined by the following claims construed in light of the prior artso that modifications or changes may be made to the exemplaryembodiments of the present invention without departing from theinventive concepts contained herein.

1. A data storage device, comprising: a first substrate and a secondsubstrate, wherein at least the first substrate has defined thereon aplurality of pits and lands covered by a reflective material; and abonding layer between the first and second substrates including areactive agent that interferes with the passage of light in response topredetermined stimulus, wherein the optical properties and thethicknesses of the second substrate and the bonding layer define anoptical path length relative to the pits and lands of the firstsubstrate for a light of predetermined wavelength that is external tothe second substrate, wherein the optical path length is about 0.845 mmor greater but less than about 1.039 mm.
 2. A data storage device,comprising: a first substrate and a second substrate, wherein at leastthe first substrate has defined thereon a plurality of pits and landscovered by a reflective material; and a bonding layer between the firstand second substrates including a reactive agent that interferes withthe passage of light in response to predetermined stimulus, wherein thereflective properties of the reflective material deteriorate in responseto predetermined stimulus.
 3. A data storage device, comprising: a firstsubstrate and a second substrate, wherein at least the first substratehas defined thereon a plurality of pits and lands covered by areflective material; and a bonding layer between the first and secondsubstrates including a reactive agent that interferes with the passageof light in response to predetermined stimulus; and a second reactiveagent, said second reactive agent located in or adjacent to at least oneof said first substrate layer, said second substrate layer, said bondinglayer, and said reflective material, wherein said second reactive agentin response to predetermined stimulus, promotes the deterioration of thereflective properties of the reflective material.
 4. A data storagedevice, comprising: a first substrate and a second substrate, wherein atleast the first substrate has defined thereon a plurality of pits andlands covered by a reflective material; and a bonding layer between thefirst and second substrates including a reactive agent that interfereswith the passage of light in response to predetermined stimulus; whereinthe refractive index (RI) of the second substrate and the RI of thebonding layer are approximately equal.
 5. A data storage device,comprising: a first substrate and a second substrate, wherein at leastthe first substrate has defined thereon a plurality of pits and landscovered by a reflective material; and a bonding layer between the firstand second substrates including a reactive agent that interferes withthe passage of light in response to predetermined stimulus; wherein thesecond substrate has defined thereon a plurality of pits and landscovered by a semi-reflective material, and wherein the second substratefurther includes instructions defined therein to direct an opticalreading laser to read a portion of the first substrate, prior to thelaser accessing at least a predefined portion of the second substrate.6. The device of claim 5 wherein the semi-reflective material on thepits and lands of the second substrate permits the predeterminedstimulus that reacts with the reactive agent to pass there through. 7.The device of claim 6 wherein the semi-reflective material on the pitsand lands of the second substrate is a fast deposition of asemi-reflective material.
 8. A data storage device, comprising: a firstsubstrate and a second substrate, wherein at least the first substratehas defined thereon a plurality of pits and lands covered by areflective material; a bonding layer between the first and secondsubstrates including a reactive agent that interferes with the passageof light in response to predetermined stimulus, wherein the reactiveagent interferes with the passage of light in response to oxygen;wherein the device further includes protective substance to control thetime necessary for the reactive agent to interfere with the passage oflight, said protective substance located in or adjacent to at least oneof said reactive agent, said first substrate and said second substrate.9. The device of claim 8 wherein the protective substance is a coatingof at least one surface of at least one of the first and secondsubstrates.
 10. The device of claim 8 wherein the protective substanceincludes a layer of antioxidant material disposed between the secondsubstrate and the reactive agent.
 11. The device of claim 8 wherein thereactive agent interferes with the passage of light of a predeterminedfrequency range and wherein the device further comprises material thatinterferes with the passage of light of a second predetermined frequencyrange through the material, said material located in the optical path ofa reading beam.
 12. The device of claim 11 wherein the material is acoating of at least one surface of at least one of the first and secondsubstrates.
 13. The device of claim 10 wherein the material thatinterferes with the passage of light of a second predetermined frequencyrange is included in the second substrate.
 14. The device of claim 10wherein the material that interferes with the passage of light of asecond predetermined frequency range is included in the bonding layer.15. The device of claim 10 wherein the material that interferes with thepassage of light of a second predetermined frequency range is includedin a separate layer disposed between the second substrate and thereflective material covering the pits and lands of the first substrate.16. A data storage device, comprising: a first substrate and a secondsubstrate, wherein at least the first substrate has defined thereon aplurality of pits and lands covered by a reflective material; and abonding layer between the first and second substrates including areactive agent that interferes with the passage of light in response topredetermined stimulus, wherein the device further includes protectivesubstance to control the time necessary for the reactive agent toinhibit the passage of light, said protective substance located in oradjacent to at least one of said reactive agent, said first substrateand said second substrate.
 17. The device of claim 16 wherein theprotective substance increases the time necessary for the reactive agentto inhibit the passage of light.
 18. The device of claim 16 wherein theprotective substance includes a layer of antioxidant material disposedbetween the second substrate and the reactive agent.
 19. The device ofclaim 8 wherein the protective substance increases the time necessaryfor the reactive agent to inhibit the passage of light.
 20. A datastorage device, comprising: a first substrate and a second substrate,wherein at least the first substrate has defined thereon a plurality ofpits and lands covered by a reflective material; a bonding layer betweenthe first and second substrates; a reactive agent that, in response topredetermined stimulus, interferes with the passage of light of apredetermined frequency range, said reactive agent located in theoptical path of a reading beam; and material that interferes with thepassage of light of a second predetermined frequency range through thematerial, said material located in the optical path of the reading beam.21. The device of claim 20 wherein the material is a coating of at leastone surface of at least one of the first and second substrates.
 22. Thedevice of claim 20 wherein the material that interferes with light of asecond predetermined frequency range is included in the secondsubstrate.
 23. The device of claim 20 wherein the material thatinterferes with light of a second predetermined frequency range isincluded in the bonding layer.
 24. The device of claim 20 wherein thematerial that interferes with light of a second predetermined frequencyrange is included in a separate layer disposed between the secondsubstrate and the reflective material covering the pits and lands of thefirst substrate.
 25. A data storage device, comprising: a firstsubstrate and a second substrate, wherein at least the first substratehas defined thereon a plurality of pits and lands covered by areflective material, wherein the reflective properties of the reflectivematerial deteriorate in response to predetermined stimulus; a bondinglayer between the first and second substrates; including a reactiveagent that, in response to predetermined stimulus, interferes with thepassage of light of a predetermined frequency range, said reactive agentlocated in the optical path of a reading beam.
 26. A data storagedevice, comprising: a first substrate and a second substrate, wherein atleast the first substrate has defined thereon a plurality of pits andlands covered by a reflective material; a bonding layer between thefirst and second substrates; a reactive agent that, in response topredetermined stimulus, interferes with the passage of light of apredetermined frequency range, said reactive agent located in theoptical path of a reading beam; and a second reactive agent, in responseto predetermined stimulus, promotes the deterioration of the reflectiveproperties of the reflective material, said second reactive agentlocated in or adjacent to at least one of said first substrate layer,said second substrate layer, said bonding layer, and said reflectivematerial.
 27. An optically-readable storage media, comprising asubstrate having encoded data stored thereon; a reactive agent that, inresponse to predetermined stimulus, interferes with the passage of lightof a predetermined frequency range said reactive agent located in theoptical path of a reading beam; and material that interferes with thepassage of light of a second predetermined frequency range through thematerial, said material located in the optical path of the reading beam.